1. Field of the Invention
The present invention relates to a data communication apparatus for setting a data transmission rate in accordance with a communication processing ability.
2. Related Background Art
An apparatus of this type has been known as a facsimile apparatus, for example.
In a prior art facsimile apparatus, when a receiving facsimile apparatus has a modem of V.29 and V.27 ter (9600 bps, 7200 bps, 4800 bps and 2400 bps), a transmission rate ability of the modem is informed by a protocol signal to a transmitting facsimile apparatus. The transmitting facsimile apparatus selects from the received transmission rate ability of the receiving apparatus a highest transmission rate which is compatible to its own modem and informs the selected transmission rate to the receiving apparatus and sends a training check signal (TCF) for checking whether an image signal can be transmitted at the selected transmission rate. If the receiving apparatus correctly receives the TCF signal at the selected transmission rate, it informs to the transmitting apparatus the normal reception of the TCF signal. Subsequently, the image is communicated at the selected transmission rate. On the other hand, if the receiving apparatus does not correctly receive the TCF signal at the selected transmission rate, it informs to the transmitting apparatus that the TCF signal was not received correctly. The transmission apparatus sets the transmission rate one step lower and retransmits the TCF signal. In this manner, the transmission rate is lowered stepwise until the TCF signal is correctly received by the receiving apparatus, and after the TCF signal is correctly received, the image is communicated at that transmission rate. In this manner, in the prior art facsimile apparatus, a transmission rate is determined in accordance with a quality of the line.
A facsimile apparatus which receives image information from an external information terminal such as a computer and sends the received image information to another facsimile apparatus has been known. In such a facsimile apparatus, a transmission rate which does not cause underflow or overflow by a receiving rate of the image information from the external information terminal, a quality of the line and a function of a destination facsimile apparatus is selected. The selected transmission rate is thereafter changed in accordance with the quality of the line. In such a facsimile apparatus, the receiving rate of the image rate from the external information terminal is determined by the data communication function between the external information terminal and the facsimile apparatus. The facsimile apparatus sets the transmission rate to the destination facsimile apparatus such that it is lower than the receiving rate from the external information terminal. Accordingly, once the receiving rate from the external information terminal is set to a low transmission rate, the communication can be conducted only at the low transmission rate even if the communication at a higher transmission rate is permitted between both facsimile apparatuses.
In the above instance, if the function of the external information terminal has only the low transmission rate, it is natural that the transmission rate between both facsimile apparatuses is low.
However, a certain external information terminal (computer) may conduct the data transmission and the data processing concurrently by the multitasking in which one CPU (microcomputer) parallelly executes a plurality of types of processing. In this case, the processing speed for the data transmission changes between when the computer is dedicated to the data transmission and when it parallelly executes the data transmission and data processing. Thus, when it is dedicated to the data transmission, the data transmission at a high transmission rate is permitted while when it transmits the data by the multitasking, only the data transmission at a low transmission rate is permitted.
When the image information is to be transmitted from the external information terminal to another facsimile apparatus through the facsimile apparatus, the low transmission rate is set if the external information terminal is processing the multitask at the start of the transmission. Even if the multitask processing is over during the transmission and the external information terminal may be dedicated to the data transmission and the high transmission rate is permitted, the image communication is conducted at the low transmission rate once it is set.
This is not only a problem where the image information of the external information terminal is transmitted to another facsimile apparatus through the facsimile apparatus but also a problem in a facsimile apparatus having a complex function of executing a local operation (such as a copy operation) and the facsimile communication by one CPU.